The present invention relates to room temperature vulcanizable organopolysiloxane compositions having improved shelf stability and a reduced tendency to corrode copper, resulting from the use of an effective amount of an inhibitor such as aryltriazole and a tin condensation catalyst having organo radicals attached to tin by carbon-tin linkages and whose remaining valences are satisfied by a .beta.-diketonate group, for example, di(n-butyl)tinbis(acetylacetonate), or a dicarboxy radical such as diethylmalonate or dicarboxy hexahydrophthalate.
Prior to the present invention as shown by Brown et al, U.S. Pat. No. 3,161,614, attempts were made to make stable room temperature vulcanizable (RTV) compositions employing a polyalkoxy end blocked polysiloxane and a monocarboxylic acid metal salt catalyst, such as dibutyltindilaurate. These compositions did not cure satisfactorily. Improved results were obtained by Beers, U.S. Pat. No. 4,100,129, assigned to the same assignee as the present invention, utilizing as a condensation catalyst, a silanol reactive organometallic ester having organo radicals attached to metal through metal-oxygen-carbon linkages. Experience has shown that in instances where silanol reactive organo tin compounds are used as RTV condensation catalysts which have organo radicals attached to tin by tin-oxygen-carbon linkages, the resulting moisture curable compositions are often unstable.
As utilized hereinafter, the term "stable" as applied to the one package polyalkoxy-terminated organopolysiloxane RTV's of the present invention means a moisture curable mixture capable of remaining substantially unchanged while excluded from atmospheric moisture and which cures to a tack-free elastomer after an extended shelf period. In addition, a stable RTV also means that the tack-free time exhibited by freshly mixed RTV ingredients under atmospheric conditions will be substantially the same as that exhibited by the same mixture of ingredients exposed to atmospheric moisture after having been held in a moisture resistant and moisture-free container for an extended shelf period at ambient conditions, or an equivalent period based on accelerated aging at an elevated temperature.
Further advances were achieved with the employment of silane scavengers for eliminating chemically combined hydroxy radicals, water, or methanol, as shown by White et al, U.S. Pat. No. 4,395,526, assigned to the same assignee as the present invention and incorporated herein by reference. However, the preparation of these silane scavengers, such as methyldimethoxy-(N-methylacetamide)silane often requires special techniques and undesirable by-products can be generated during cure. Further improvements are shown by Dziark for scavengers for one component alkoxy functional RTV compositions and process, U.S. Pat. No. 4,417,042, assigned to the same assignee as the present invention and incorporated herein by reference.
In copending application Ser. No. 583,530, now U.S. Pat. No. 4,517,337 it was found that tin condensation catalyst having organo radicals attached to tin by carbon-tin linkages whose remaining valences satisfied by a .beta.-diketonate group, for example, di(n-butyl)tinbis(acetylacetonate) could be used as a condensation catalyst in room temperature vulcanizable organpolysiloxane compositions as described above without the employment of a scavenger for trace amounts of water, methanol and silanol.
As shown in copending application Ser. No. 644,891, improvements have been achieved with respect to reducing the tendency of RTV compositions to corrode copper under vapor phase corrosion conditions, while still maintaining a stable RTV formulation, without the employment of a scavenger, by utilizing as the tin condensation catalyst, an effective amount of a tin compound having organo radicals attached to tin by carbon tin linkages and whose remaining valences are satisfied by a dicarboxylate radical, such as diethylmalonate or hexahydrophthalic dicarboxylate as defined more particularly below. As used hereinafter, the expression "vapor phase corrosion" means corrosion, as shown by a change in color, occurring on a brass strip (85% by weight of copper) which is suspended above a mixture of 15 parts by weight of uncured RTV and 5 parts of water in a closed container.
Even though RTV formulations can exhibit an ability to resist copper corrosion under vapor phase corrosion conditions, unacceptable corrosion also can occur when such RTV in the cured state is allowed to contact metallic copper at ambient conditions for an indefinite period of time.
The present invention is based on the discovery that significant improvements with respect to contact copper corrosion can be achieved with RTV organopolysiloxane formulations comprising the combination of an effective amount of a tin condensation catalyst having the formula EQU (R).sub.2 Sn[Y'], (1)
and a copper corrosion inhibitor as defined hereinafter, which is capable of retarding the corrosion of metallic copper, when in contact with the RTV in the cured state at ambient temperatures over an extended period of time, where R is selected from C.sub.(1-18) monovalent hydrocarbon radicals and substituted C.sub.(1-18) monovalent hydrocarbon radicals, and Y' is a divalent radical selected from
(i) a chelate group having the formula ##STR1##
(ii) and a dicarboxylate group having the formula ##STR2## R.sup.1, R.sup.2 and R.sup.3 are the same or different monovalent radials selected from the class consisting of hydrogen, R, --Si(R).sub.3, acyl and nitrile, R.sup.4 is selected from divalent C.sub.(1-18) hydrocarbon radical and substituted divalent C.sub.(1-18) hydrocarbon radicals.